The present invention relates in general terms to a cooling/heating circuit for a vehicle and especially but not exclusively for a vehicle with an electric motor fed by a fuel cell.
In a generally customary manner, a cooling/heating circuit comprises a cooler, which serves to give off heat to the environment. For this purpose, the assembly to be cooled, e.g. the engine or a fuel cell, is brought into thermal interaction with a coolant fluid, whether directly or via a further heat exchanger circuit, the fluid generally being conveyed in the cooling/heating circuit by a pump driven mechanically or by an electric motor. To heat the interior of the motor vehicle, a heat exchanger is conventionally either integrated directly into the cooling/heating circuit or, as in solutions which are already known, a secondary circuit which transfers the heat from the cooling/heating circuit to a heating element is provided for heating purposes. An arrangement of this kind is described, for example, in EP-0 638 712.
However, it has recently been found that, particularly in the case of electric vehicles with a fuel cell that have a high mechanical driving power, the entire heat output to be dissipated can only be removed by a single cooler at considerable expense, if at all. In the case of the above-mentioned vehicles especially, there is a striking difference compared to vehicles driven by internal combustion engines since waste heat can be dissipated to only a minimal extent by means of the exhaust gas, if at all. Another problem results from the fact that not only is the heat output to be dissipated high and the installation space small, but also the temperature level requirements for the individual assemblies to be cooled vary very widely. For example, the operating temperature of a fuel cell is currently about 80xc2x0 C., while condensers for exhaust gases or a connected air-conditioning system, for example, which are integrated into the cooling/heating circuit, require significantly lower temperatures.
Cooling/heating circuit systems have therefore recently been developed which have two constituent circuits which are, at least in part, at different temperatures and each contain at least one cooler in order in each case to cool at least one assembly. Such a cooling/heating circuit of the generic type in accordance with the preamble of claim 1 is disclosed in xe2x80x9cWxc3xa4rmexc3xcbertrager im Brennstoffzellenfahrzeugxe2x80x94neue Anwendungen und Anforderungenxe2x80x9d [Heat exchangers in fuel-cell vehiclesxe2x80x94new applications and requirements], Brennstoffzellenfahrzeuge, Haus der Technik, Nov. 30, 1999. In the case of the concept disclosed here, a high-temperature coolant circuit is used to cool the fuel cell and the intercooler, if the latter is embodied as a liquid-cooled heat exchanger, while a low-temperature circuit cools the exhaust-gas condenser and other electronic components, where appropriate. Each of the circuits has a separate cooler, the low-temperature cooler being arranged upstream of the high-temperature cooler in terms of airflow. However, since in general the installation space available in vehicles is very limited, there is a problem both with integration and with heat dissipation in a vehicle since separate control and driving means are required for each constituent circuit. As stated by the authors, the solution described is accordingly to be regarded only as a concept proposal, and there is the further proviso that, in general, it would probably only be possible to provide a solution for small-category fuel-cell vehicles.
It is therefore the object of the present invention to specify a cooling/heating circuit which, while requiring less installation space, can also be integrated into vehicles in higher categories, especially those with a high mechanical power.
According to the invention, the above object is achieved, in the case of a cooling/heating circuit of the generic type with at least two constituent circuits which are, at least in part, at different temperatures and each contain at least one cooler in order in each case to cool at least one assembly, by virtue of the fact that the constituent circuits are coupled fluid-mechanically to one another. In other words, there is an interrelationship at least as regards the flow in the constituent circuits involved, resulting in simplified common control of the respective constituent circuits and/or a fluid drive for the respective constituent circuits that requires less installation space. Any further auxiliary circuits, e.g. a thermodynamic air-conditioning circuit, a conventional and/or thermodynamic heating circuit and the like can optionally be coupled to either of the constituent circuits, although these additional circuits should not be thought of as constituent circuits according to the definition given in the above description and the attached claims.
The constituent circuits are advantageously coupled to one another either by means of a common pump, two pumps with a common drive or by means of a device that, on the basis of the flow in one constituent circuit, brings about flow in another constituent circuit. Although the use of just one pump allows a design that takes up a minimal amount of installation space, a considerable amount of installation space can still be saved if use is made of two pumps with a common drive. In addition to coupling by means of one or more pumps, there is a large number of further ways of using fluid flow in one circuit to bring about fluid flow in another circuit. Purely by way of example, mention will be made here of means based essentially on the principle of an ejector pump, and of a turbine, which, when arranged in one of the constituent circuits, allows mechanical power transmission to a pumping medium in another constituent circuit.
In a preferred embodiment, there is not only coupling in terms of flow but also thermal coupling, thus allowing temperature transfer and, in this context, it is possible, in particular, to use a common line section. The possibility of temperature transfer from one constituent circuit to another, in particular from a constituent circuit at a lower temperature to a constituent circuit at a higher temperature, advantageously makes it possible to compensate for thermal peaks in the constituent circuit at higher temperature or to provide a region at moderate temperature in the latter. It should be mentioned that the thermal coupling can be provided either by mixing fluid or without exchanging fluids, e.g. by means of a heat exchanger.
In order to take account of the respective operating states of the assemblies to be cooled and/or constituent circuits, the coupling in terms of flow and/or the temperature transfer between the constituent circuits can be made controllable. This control can be achieved in a particularly simple manner by means of adjustable valves, although other means, e.g. transmissions with various transmission ratios, are also possible where, for example, two pumps with a common drive are provided.
In a particularly preferred embodiment, the fluid-mechanical and/or temperature coupling takes the form of one constituent circuit acting as a control circuit for the other constituent circuit. If, for example, a low-temperature circuit is provided as a control circuit for a high-temperature circuit, an appropriately arranged metering valve can be used to take fluid from a temperature circuit at high temperature to enable it to be cooled significantly in the low-temperature constituent circuit, so that this lower-temperature fluid can be fed back into the original constituent circuit.
In a particularly preferred embodiment of the present invention, at least one of the assemblies to be cooled comprises a fuel cell, which is associated with one of the constituent circuits via a heat exchanger, for example. Most currently available fuel cells require the use of deionized water, leading to the use at present of an auxiliary circuit with a heat exchanger.
It is furthermore advantageous if at least one of the assemblies to be cooled is an air-conditioning condenser, which is, in particular, arranged at the coolest point in the cooling/heating circuit. It is a well-known fact that air-conditioning condensers require a relatively low temperature level, for which reason air-conditioning systems have generally not been provided in fuel-cell vehicles up to now. However, since high-class vehicles with a correspondingly high engine output are now in demand, it is necessary in terms of vehicle comfort to provide an air-conditioning system for such vehicles.
It is advantageous if at least two, in particular in each case two, assemblies to be cooled from the group comprising the intercooler, the fuel cell or fuel-cell heat exchanger, the exhaust-gas condenser and the fuel cooler, are connected directly in series in a constituent circuit. In particular, it is, for example, advantageous if the intercooler and fuel cells are connected directly in series since, ideally, the air to be fed to the fuel cell should be approximately at the operating temperature of the fuel cell. The same applies to the fuel cooler and it is therefore advantageous to connect it in series with the intercooler and/or the fuel cell.
It is advantageous for at least two, in particular three, assemblies to be cooled which have a low heat output and/or require a low temperature level to be provided in parallel in one of the constituent circuits. In particular, these assemblies can be an intercooler, an air-conditioning condenser, a fuel cooler, an inverter or even the electric motor itself.
Since certain assemblies to be cooled, e.g. the air-conditioning condenser, the exhaust-gas condenser and the intercooler require relatively low temperatures and/or a relatively small cooling capacity, it is preferred that at least one, in particular two, of the above-mentioned assemblies should be connected upstream of the assembly to be cooled with the highest heat output, which will usually be the fuel cell in the case of a fuel-cell vehicle.
To enable the different temperature levels of the constituent circuits coupled in terms of flow, which can optionally also be coupled thermally subject to certain conditions, to be exploited in an optimum manner, it is preferred that at least one, in particular two, assemblies to be cooled which have a low heat output and/or require a relatively low temperature, selected from the group comprising the air-conditioning condenser, the exhaust-gas condenser and the intercooler for example, is/are arranged in a constituent circuit which does not contain the assembly to be cooled with the highest heat output.
Finally it is preferred that the coolers in different constituent circuits should be arranged in separate air ducts. In the case of two constituent circuits, for example, it would be possible to arrange the cooler of the low-temperature constituent circuit in a decentralized manner, i.e. at a different location from that of the conventional cooler in known vehicles.